Fixing DNS issues

I've noticed some slow DNS on my station for the last few weeks and finally got down to checking it out. In the wake of the cache-poisoning scare of late July, we had to upgrade our DNS servers to something a bit less scarily old. I believe this required an operating system rev. The last time this happened to me, we figured out that the DNS server in question had auto-negotiated itself to 10-HalfDuplex, and the switch thought it was 100-FullDuplex. You can imagine what that did to throughput.

I fired up wireshark and started tracking my DNS requests. A pattern soon emerged. The first entry in my resolve.conf list was taking anywhere from .5 to 5.2 seconds to resolve most queries. This is hella slow for a DNS server. Since I don't manage these machines, I let the admin who did manage 'em know about it. He couldn't find anything wrong with the DNS servers on a first glance.

Another thing I noticed when looking at the resolver requests I was passing was a lot of IPv6 requests. Almost all of them were for Active Directory related queries, as I've turned off IPv6 support in my web-browser. I still haven't quite figured out how to disable IPv6 on my openSUSE 10.3 machine here.

As it happens, said DNS admin came back in and said to look at things again. So I dropped into nslookup and started throwing queries and watching the response times in wireshark, and sure enough they were zippy again. He turned off IPv6 support on the DNS servers.

Looks like we'll probably need to have a conversation on campus about IPv6 sooner rather than later. Vista comes with it turned on by default, and happily we don't have much of that yet. But these newer linux distros all have it turned on by default.